The spectrograph is the time-honored tool for study of speech perception for visually displaying segregated frequency patterns in space. Recently, however, there is evidence to show that many differences exist between a speech spectrograph and a neural output of a cochlea. For example, the output of the cochlea is linear up to about 1,000 Hz and logarithmic above that, whereas the spectrograph is either logarithmic or linear. Thus, there is serious question whether the temporal processing of acoustical components of speech by the ear can be demonstrated by a speech spectrogram. This is not considered to be a trivial shortcoming of the speech spectrogram given that the fundamental frequency and the first formant information of speech are coded, at least to some extent, by temporal information.
Although it can now be shown that there is a basic problem with the use of the speech spectrogram for voice analysis, the primary problem appears to be that the exclusive use of the spectrograph for speech analysis confines the concept of the speech signal to a spatio-temporal display. Such a spatio-temporal display is now realized to be quite unlike the signal as it exists in space. An acoustic speech signal does have spatial property, but they are not necessarily related to the spatial separation frequencies manifested in the speech spectrogram. The acoustic speech signal is a frequency-integrated, complex waveform whose actual spatial properties are indicated by radiation and reflection, not by frequency. The acoustic world we live in is not fully represented by a speech spectrogram.
Heretofore, the reliance on the speech spectrograph as the sole source of information about the speech signal has restricted observations to an analog of the neural output of the cochlea. This has resulted in the missing of the hypothesized higher order free integration stage of perceptual analysis. It is now understood that a more complete analysis of a speech signal required a study of the speech waveform in addition to the spectrogram. The spectrogram provides the components of the signal (spatial) and the waveform shows how the components are integrated in time and space.
A feature of the present invention is to provide apparatus for analyzing the speech waveform for kinds of information not readily observable from the spectrogram. Further, by the apparatus of the present invention, information available from the speech waveform can be applied to practical problems in speech science. Specifically, by examining the speech waveform, there is developed a tactile speech reception aid for the deaf.
Further, an examination of the speech waveform has been applied to the invention described and claimed in the co-pending patent application entitled, "Voice Pitch Detector and Display", Ser. No. 48,238, filed June 13, 1979, which is a real time speaker independent pitch extractor with a voice pitch display. A voice pitch detector and display as described in applicant's co-pending application is a device which integrates the periodicities of several spectral channels to aid in the perception of pitch.
In accordance with the present invention, there is provided a tactile aid to speech reception which presents information about a speech signal to an observer through the skin by means of vibrator transducers. The tactile aid utilizes the waveform envelope to provide a single, slowly varying reference for the many rapid spectral changes in speech. This provides the perceptual system of the observer with a means of integrating information over relatively long periods of time (across syllables). The importance of this is to maintain the temporal order of the speech elements for the observer. The aid of the present invention develops a single time envelope for the integration of spectral information by means of discretely placed vibrators.
Heretofore, tactile aids utilized vocoder type transducers for the conveyance of tactile speech cues. Vocoder type aids separate spectral information into spatially arrayed areas on the skin. Such type aids encounter difficulties when ordering spectral information in time, since the vocoder type aid has as many separate time envelopes as it has spectral channels. It is believed that the vocoder type aid provides good vowel discrimination whereas the vibrator type aid of the present invention has the advantage of discriminating sentence length material.
A feature of the present invention is to provide a tactile aid to speech reception that retains an integrated amplitude envelope and enables the observer to discriminate sentence length material. Further, in accordance with the present invention, a tactile aid conveys as much spectral information to the skin as possible without sacrificing the waveform envelope.